1. Field of the Invention
The present invention generally relates to the art of electrochemical cells and, more particularly, to a lithium-containing cell with an electrically conductive counter-collector fabricated by a new continuous feed apparatus. In general, it has been discovered that electrically conductive materials, such as of a carbonaceous chemistry, can readily be compressed onto the opposed major sides of a perforated conductive collector substrate without sloughing off or delaminating. This makes the resulting carbonaceous laminate particularly useful as a cathode collector in lithium/oxyhalide cells.
2. Prior Art
Primary lithium oxyhalide cells are used extensively in applications requiring high gravimetric and volumetric energy density. Among the many sizes and chemistries available, cells can be developed for low rate or high rate applications and to operate from temperatures as low as −70° C. to as high as 200° C. The anode material usually consists of lithium or lithium alloyed with various elements such as aluminum, magnesium or boron and the cathode collector usually consists of some form of carbon held together using a suitable binder. The electrolyte generally consists of a solvent system of thionyl chloride, phosphoryl chloride or sulfuryl chloride. Often, additional compounds or interhalogen compounds such as sulfur dioxide, chlorine, bromine, bromine chloride and others may be dissolved therein to modify the cell for a particular purpose, such as extending the operating rate or temperature of the cell. Electrolyte salts are also added to the solvent system to assist in ionic transfer during cell discharge. Such salts may include lithium chloride in combination with aluminum trichloride or gallium trichloride. Lithium tetrachloroaluminate salt (LAC) or lithium tetrachlorogallate salt (LGC) is then formed in-situ. Typically used catholytes include chlorinated sulfuryl chloride (CSC) having either LAC or LGC dissolved therein. These systems are commonly referred to as LAC/CSC and LGC/CSC.
The liquid oxyhalides of the elements of Group V or Group VI of the Periodic Table are liquid active reducible cathode materials (depolarizer). As used herein and as disclosed in an article titled “Electrochemical Reactions in Batteries” by Akiya Kozawa and R. A. Powers, in the Journal of Chemical Education—Vol. 49, pages 587 to 591, September, 1972 edition, a cathode depolarizer is the cathode reactant and, therefore, is the material electrochemically reduced at the cathode collector. The cathode collector is not an active reducible material and functions as a current collector plus electronic conductor to the cathode terminal of the cell. In other words, the cathode collector is a situs for the electrochemical reduction reaction of the active cathode material and the electronic conductor to the cathode terminal.
A liquid active reducible cathode material (depolarizer) can either be employed by itself in an electrochemical device (i.e. galvanic cell), mixed with a conductive solute, which is a non-reactive material but is added to improve conductivity of the liquid active reducible cathode materials, or mixed with both a conductive solute and a reactive or non-reactive co-solvent. A reactive co-solvent material is one that is electrochemically active and, therefore, functions as an active cathode material while a non-reactive co-solvent is one that is electrochemically inactive and, therefore, cannot function as an active cathode material.
Any compatible solid which is substantially electronically conductive is useful as the cathode collector. However, it is desirable to have as much surface contact as possible between the cathode-electrolyte and the collector, and a pressed carbonaceous powder collector that provides a high surface area interface with the liquid cathode electrolyte is preferred. This means that the manufacturing process needs to produce collectors having uniform carbonaceous basis weights, which is defined as the gram amount of the carbonaceous material per unit volume, with little thickness variability across the collector sheet. Cells exhibiting consistent discharge performance from one cell to the next result when strict tolerances for these parameters are maintained.